(62g) Foam Decay with Knitted Wire Mesh – Overview about Characterization, Decay and Prevention of Foam

Armin Pitzer, Rhodius GmbH

Stefan Hegner, Rhodius GmbH

Wolfgang Heikamp, Rhodius GmbH

The occurrence
of foam in chemical industry, e.g. in packing columns, can cause many problems,
such as additional pressure drop, low mass transfer and consequently low
capacity. To prevent foaming in general you can use chemical, thermal or
mechanical procedures. The intention of RHODIUS is to destroy foaming by
mechanical forces using knitted wire mesh.

The
presentation starts up with the characterization and formation of foam.  It is
a dispersion of gas in liquid generated by gassing, beating or the drop down of
liquids. In general this dispersion is split in three different parts. On the
top you can find metastable or polyhedron foam. Here the gas fraction, which is
defined by  is
≥ 0,74. The layer below is called spherical foam (0,52 ≤  ≤
0,74). On the bottom you will find the gas/liquid dispersion ( ≤
0,52).

The
decay of foam is attended to its stability. There are several methods to
investigate the foam stability like the Bikerman or the Ross-Miles
method.

Moreover,
foams are thermodynamically instable systems. The driving force for the
instability is the growth of interface surface energy. There are three
different processes that lead to the minimization of free energy.

Firstly,
the diffusion of gas between neighboring bubbles. Secondly, the drainage of
interlamellar fluid and finally the coalescence of bubbles.

In
recent experimental studies with standard available knitted wire mesh we
investigate the influence of installed porous media on:

-
conveying coalescence by static internals

- mechanical
energy generated by pressure drop

 leading
to the destruction of foam.